1. Field of the Invention
This invention relates to polyurethanes and more particularly to rigid, dense, rapid-setting polyurethane molded compositions.
2. Description of the Prior Art
Rapid-setting polyurethane compositions are disclosed in U.S. Pat. No. 3,378,511 in which there is disclosed the reaction of a polyether polyol and a polyisocyanate in the presence of a modifying composition consisting of an ester such as dioctylsebacate, dioctylphthalate, and mixtures thereof. Rapid-setting polyurethane casting compositions have also been prepared in the prior art by substituting for the ester type plasticizer such as dioctylphthalate various diluents which prevent excessive bubbling which would, in their absence result from the heat generated by the exothermic heat of reaction. Generally, liquids known in the prior art which are useful as liquid modifying compositions have boiling points at atmospheric pressure above about 150 degrees centigrade and are illustrated by such compounds as fatty acids and oils, organic phosphates, such as tricresylphosphates, phosphites and phosphonates; cyclic polyethers, aromatic compounds free from ester groups (1-chloronaphthalene), halogenated aliphatic compounds (chlorinated paraffins), hydroxyl containing halogenated aliphatic compounds, cyclic sulfones (3-methylsulfonolane), and organic carbonates (propylene carbonate). The polyurethane compositions of the prior art are generally characterized as opaque as a consequence of the presence in substantial proportions of at least two phases. Representative U.S. Pat. Nos. are 3,746,692; 3,726,827; 3,801,532; 3,878,156; 3,725,355; 3,882,071; 3,883,465, 3,883,466; 3,883,484; 3,886,102; 3,886,182 and 3,914,918.